This invention relates to a self-drilling pull-through blind rivet, and methods of and apparatus for the assembly and setting thereof. In particular, this invention relates to an unset self-drilling pull-through blind rivet which is structured to form a hole in a workpiece for facilitating the locating of the unset rivet therein. This invention further relates to methods of and apparatus for assembling and setting the unset rivet relative to the hole formed thereby.
A known unset rivet, or rivet body, is formed with a cylindrical portion having an axial passage, of constant diameter, formed therethrough. A first axial, or forward, end of the rivet body is a continuation of the cylindrical portion, while a second axial, or trailing, end is formed with a flange.
In one step of a known process for assembling and setting the rivet body to secure workpieces, an operator drills, or preforms, aligned holes in the workpieces. In another separate step of the known process, and using a known tool, the operator facilitates the advancement of successive rivet bodies into successive respective sets of the aligned preformed holes. Thereafter the operator facilitates the setting of the rivet bodies to form set rivets, which secure the workpieces together.
In particular, in the one step, the aligned holes are preformed in the workpieces with a diameter which facilitates eventual placement of the cylindrical portion of the rivet body therein. In the other step, a plurality of unset rivet bodies are placed, in an axial stack, on a mandrel. The mandrel includes an enlarged setting head at a forward end thereof adjacent the first rivet body of the stack. The enlarged head has a diameter greater than the diameter of the axial passage of the rivet bodies, but less than the diameter of the cylindrical portion of the rivet bodies. With this arrangement, the enlarged head precludes forward movement of the first rivet body, and the rivet bodies which follow axially behind the first rivet body. A trailing end of the mandrel is formed with a grippable structure, which facilitates gripping thereof by a gripping means within the tool.
The mandrel and the rivet bodies stacked thereon are assembled within the tool, with the enlarged setting head and the first rivet body extending from a forward end of the tool. The trailing end of the mandrel is gripped within the tool, and a forward force is applied to the flange of the last, or trailing-most, rivet body to selectively urge the stack of rivet bodies in a forward direction, and thereby maintain the rivet bodies in a tightly stacked condition during successive rivet-setting operations.
The enlarged setting head of the mandrel and a cylindrical section of the first rivet body, excluding the flange thereof, are inserted into the respective aligned holes, which have been independently preformed in the workpieces. The flange of the first rivet body engages one of the workpieces to preclude further advancement of the rivet body. In this inserted position, the mandrel head and a leading portion of the cylindrical portion at the first axial end extend forward beyond the aligned holes.
Thereafter, while the first rivet body is precluded from retraction, the mandrel is retracted axially from within the tool to pull the setting head of the mandrel through the first rivet body, from the leading end to the trailing end of the rivet body. As the head of the mandrel is pulled rearward through the leading end of the first rivet body, the head expands, or distends, the material of the extended leading portion of the cylindrical portion. The expanded material is substantially larger than the hole in the adjacent workpiece, and forms a blind-side bulge in the rivet body, which is in engagement with the adjacent workpiece. The reshaping of the rivet body, to form the blind-side bulge, results in the formation of a set rivet, which secures the workpieces together.
After the setting of the first rivet, the operator shifts the tool to another set of aligned preformed holes of the same or different workpieces and processes the second rivet body of the stack through the same steps noted above with respect to the first rivet body to set the second rivet. This process is continued for the remaining rivet bodies of the stack. Thereafter, a second plurality of rivet bodies can be stacked on the mandrel, and processed for assembly and setting.
Examples of tools and processes of the above-described type are disclosed in (1) European Patent Application No. 93303555.2, which was published on Nov. 24, 1993, as Publication No. 0 571 110, and (2) UK Patent Application GB 2 299 288, which was published on Oct. 2, 1996, both of which are incorporated herein by reference thereto.
With the above-described rivet bodies, the aligned holes must be formed through the workpieces separately and independently from the process of assembling the rivet bodies with the workpieces, thereby necessitating a multiple step process. This multiple step process is time consuming and costly, particularly when each set of aligned holes must be drilled separately and independently from the assembly of the successive rivet bodies within the respective holes. Also, care, and time, must be taken when locating and aligning the enlarged head of the mandrel in preparation for insertion of each of the stacked rivet bodies into the respective holes.
Another known tool and process for setting rivets includes a mandrel in which the forward end thereof is formed with an enlarged head having a drill point, and is useable for the setting of a single rivet only.
In use, a single rivet body is placed on the mandrel and is precluded from forward movement by the enlarged head. The mandrel, with the single rivet body thereon, is rotated about its axis and is urged forward through two workpieces to be secured together, whereby the drill point forms aligned holes therethrough. The aligned holes are formed with a diameter sized to allow passage therethrough of the enlarged head and a leading section of the cylindrical portion, and to receive the remainder of the cylindrical portion of the rivet body. Eventually, the flange of the rivet body engages an outboard surface of the adjacent workpiece to preclude further forward axial movement of the rivet body. In this inserted position, the drill point, the head and the leading section of the cylindrical portion of the rivet body extend axially outward from the aligned holes of the workpieces.
Rotation of the mandrel is stopped and the rivet body is precluded from rearward or retracting movement. The mandrel is retracted axially for a prescribed distance, whereby the enlarged head is pulled into engagement with, and expands, the leading section of the cylindrical portion of the rivet body. The expanded material of the leading section of the cylindrical portion is now substantially larger than the hole in the adjacent workpiece thereby to form a blind-side bulge in the rivet body, which is in engagement with the adjacent workpiece. A set rivet is thereby formed and the workpieces are secured together.
During the setting of the rivet, the drill point and the enlarged head of the mandrel are retracted or pulled for the prescribed distance, whereby the drill point and the enlarged head remain on the blind side of the workpieces. If the enlarged head was pulled or retracted farther than the prescribed distance, and thereby into the section of the cylindrical portion which is located within the drilled holes, the material of the section would be compromised to the extent that the rivet would be ineffective to secure the workpieces together.
Therefore, after the mandrel has been pulled for the prescribed distance, and the rivet has been set, the mandrel, the drill point and the enlarged head are not recoverable, and remain with the set rivet or can be pushed through the set rivet and discarded on the blind side of the secured workpieces. In any event, the mandrel, with the head and drill point, can not be used thereafter for a rivet-setting operation. With this system, then, each mandrel with the drill point and the enlarged head can be used only once to assemble and set a single rivet. This process is a time consuming and expensive manner of assembling and setting rivets.